LOS ANGELES (Reuters) – American country music stars were gripped by fear and horror after Sunday’s mass shooting in Las Vegas turned a three-day open-air festival attended by some 22,000 people into a scene of carnage.

The Route91 Harvest festival, promoted as a “three day neon sleepover,” attracted fans from across the United States to hear country’s biggest stars, including Jason Aldean, Eric Church and Sam Hunt.

Aldean, the Sunday night headliner, had just taken the stage when bursts of gunfire rang out, sending thousands of people diving for cover.

At least 58 people were killed by a 64-year-old gunman who released a hailstorm of bullets into the festival site. Police said the gunman’s motives remain unknown.

“Tonight has been beyond horrific,” Aldean, 40, who was unharmed, said on Instagram. “It hurts my heart that this would happen to anyone who was just coming out to enjoy what should have been a fun night.”

Singer Jake Owen, who performed minutes before Aldean, said he witnessed “the most unimaginable event.”

“Shots were ringing off the stage rigging and road cases. No one knew where to go,” Owen tweeted.

Owen told Fox News in an interview early on Monday, ”This isn’t what America is supposed to look like.

“We put on concerts to take people away from the day-to-day life, to bring them to a happy place, and this isn’t by any means what’s supposed to happen at these things,” Owen said.

Chris Young, a country singer who was at the festival on Sunday but not playing, said on Twitter that he “spent I don’t know how long on the floor of a trailer behind the stage” listening to the gunfire.

“I‘m literally shaking still,” Young added.

Country newcomer Kane Brown, 23, who performed earlier on Sunday, tweeted, “This world is sick.”

The Route91 festival has been held in Las Vegas for three years, attracting large crowds to hear country music’s top talent. The festival was open to all ages, with strollers welcome. Tickets for the 2017 event started at $210 for three days, rising to $750 for an air-conditioned VIP suite, according to the festival website.

Photos taken earlier in the weekend and posted on the festival’s Twitter feed showed crowds of mostly young people in T-shirts and cowboy hats, dancing and drinking in the sunshine.

Festival promoter Live Nation did not return calls for comment on Monday.

Taylor Swift, who started her career as a country singer, said on Twitter there were “no words to express the helplessness and sorrow my broken heart feels for the victims.”

Luke Bryan, Miranda Lambert and Shania Twain tweeted that they were heartbroken, while veteran singer Brad Paisley said “there are no words right now that suffice,” and Keith Urban said he was “stilled and speechless.”

On Monday afternoon, the website for the Route91 festival remained unchanged, with no mention of mass shooting. “Passes are sold out,” it said.